Polishing apparatus, polishing pad, and polishing method

ABSTRACT

A polishing pad is placed on a polishing apparatus including a polishing platen which is rotatable and on which the polishing pad is placed, a substrate retaining mechanism, and a supplying mechanism for supplying a polishing agent on an upper surface of the polishing pad, the polishing pad having grooves extending from the center of the polishing pad to the outer edge thereof, the groove becoming gradually deeper from the center of the polishing pad toward the outer edge portion thereof so that the depth of the groove is the largest at the outer edge portion, thereby allowing a slurry to be smoothly discharged from the upper surface of the polishing platen.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polishing apparatus for polishing a surface of a semiconductor substrate by a chemical mechanical polishing (CMP) method, a polishing pad for use in the polishing apparatus, and a polishing method using the polishing pad.

2. Description of the Related Art

In order to flatten irregularities on a surface of a semiconductor substrate in a manufacturing process of the semiconductor substrate or a manufacturing process of a semiconductor device, a chemical mechanical polishing (CMP) method is performed. For the chemical mechanical polishing method, a CMP apparatus 2 as shown in FIGS. 1 and 2 is used. The CMP apparatus 2 includes a polishing platen 4, a spindle carrier 8, a spindle 10, and a slurry nozzle 14. To an upper surface of the polishing platen 4, a polishing pad 6 is adhered. The spindle carrier 8 retains a wafer 12, that is, a semiconductor substrate, and presses the wafer 12 to the polishing pad 6 at a constant load. The slurry nozzle 14 drops the muddy slurry 16 including a polishing agent on an upper surface of the polishing pad 6. The polishing platen 4 and the spindle 10 are rotated by a rotation mechanism (not shown). The CMP apparatus 2 includes two sets of the spindle carriers 8 and the spindles 10 such that two wafers 12 can be polished at the same time. The two spindles 10 are connected to a structural body called a bridge 18.

In a polishing process for a surface of the wafer 12, the polishing agent in the slurry 16 is kept in minute holes (around 10 to 50 μm in diameter) on the surface of the polishing pad 6 and irregularities on the surface of the wafer 12 are smoothed by the polishing agent.

FIG. 3 is a top view of the polishing pad 6. FIG. 4 is a sectional view of the polishing pad 6. The polishing pad 6 has a disk shape and is made of a synthetic resin such as polyurethane. The polishing pad 6 has pad grooves 20 formed in a grid like fashion. FIG. 4 is the sectional view taken along the line A-A′ of FIG. 3. A sectional shape of the pad grooves 20 is a U-shape. A pad groove base portion 20 a is a plane. A pad groove wall 20 b is a wall perpendicular to the pad groove base portion 20 a.

A width W1 of the pad groove 20 and a depth D1 of the pad groove 20 have the same dimensions independent of the position on the pad. Further, a pitch P1 of the pad grooves 20 is constant, and the pad grooves 20 are formed in grid like fashion.

Note that, the polishing pad 6 is composed of two layers, that is, an upper layer polishing pad 6 a and a lower layer polishing pad 6 b. The upper layer polishing pad 6 a is formed with the pad grooves 20.

By performing polishing, the minute holes on the surface of the polishing pad 6 are worn out. Accordingly, the surface of the polishing pad 6 is ground by a disk plate on which diamond particles are electrodeposited, thereby creating a new surface having minute holes. This is an operation for eliminating clogging on the surface of the polishing pad 6. Thus, this operation enables to polish the wafer 12 accurately in a stable manner.

Further, as long as the slurry 16 on the pad is fresh and frequently replaced with supplying slurry, it is possible to polish the wafer 12 in a stable manner. In other words, when the slurry 16 which has been supplied from the nozzle remains on the surface of the polishing pad 6 and is not replaced with the fresh slurry 16 to be supplied later, the wafer 12 cannot be polished. Further, for accurately polishing the wafer 12, it is also important to discharge the shavings produced during polishing smoothly from the top surface of the polishing pad 6 to an outside through an outer edge of the polishing pad 6.

JP 2001-121405 A discloses a polishing pad having a structure in which a polishing surface of the polishing pad is formed with grooves extending from an initial point in the vicinity of a central portion of the polishing surface to an end point on an outer edge of the polishing surface. The cross section of a groove on the polishing pad varies between the initial point and the end point, the cross section reaches the maximum value at a point between the initial point and the end point.

JP 2005-183711 A discloses a polishing pad having a plurality of parallel groove groups including substantially straight grooves which are in parallel with each other in a polishing surface. At least one of the grooves has different depths within the same groove.

JP 2000-117620 A, JP 2004-327567 A, and U.S. Pat. No. 6,093,651 each discloses a technology of changing a depth of a groove concentrically with respect to a polishing pad from a center to an outer periphery thereof.

However, the inventor of the present invention has noticed that there are the following problems with use in those polishing pads.

In a case where a surface of the polishing pad 6 is roughly divided from a center 6 c toward an outer edge into a central portion, a middle portion, and an outer edge portion, when an operation of periodically grinding the polishing pad 6 with the disk plate as described above and a normal operation of polishing the wafer 12 are performed, the middle portion is worn down to a maximum degree, so the surface of the polishing pad 6 corresponding to the middle portion is recessed. In particular, in the operation of grinding the polishing pad 6 with the disk plate, the middle portion of the surface of the polishing pad 6 is worn down more than in the other operation.

When the middle portion of the polishing pad 6 is worn, the slurry 16 and the shavings produced by the polishing pad 6 are not discharged to the outside, and remain in the middle portion. As a result, the shavings generate minute flaws (micro scratches) on the surface of the wafer 12. Further, when the slurry 16 which is not discharged but remains on the pad, the slurry 16 is dried and then the polishing agent included in the slurry 16 becomes coarse. The coarse polishing agent may scratch the surface of the wafer 12, thereby causing the micro scratches. Accordingly, in order to ensure accuracy of a polished surface of the wafer 12 and to obtain the uniform polished surface of the wafer 12, it is important to improve discharging efficiency of the slurry 16.

However, in a case where the polishing pad 6 as shown in FIG. 3 or 4 is used, the discharging efficiency of the slurry 16 is not satisfactory. Therefore, there is a demand for the polishing pad 6, the CMP apparatus 2, and the polishing method by which the discharging efficiency of the slurry 16 is more satisfactory.

SUMMARY

According to the present invention, a polishing pad has grooves extending from a center of the polishing pad to an outer edge thereof, the groove becoming gradually deeper from the center of the polishing pad toward an outer edge thereof such that a depth of the groove is the largest at an outer edge portion. Further, the polishing pad is placed on a polishing apparatus including a rotatable polishing platen on which the polishing pad is placed, a substrate retaining mechanism, and a supplying mechanism for supplying a polishing agent on an upper surface of the polishing pad, the polishing pad having the grooves extending from the center of the polishing pad to the outer edge thereof, the groove becoming gradually deeper from the center of the polishing pad toward the outer edge portion thereof such that the depth of the groove is the largest at the outer edge portion, thereby allowing a slurry to be smoothly discharged from the upper surface of the polishing platen.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view illustrating a CMP apparatus;

FIG. 2 is a schematic side view illustrating the CMP apparatus;

FIG. 3 is a top view of a polishing pad;

FIG. 4 is a sectional view of a polishing pad according to a conventional technique;

FIG. 5A is a sectional view of a polishing pad according to a first embodiment of the present invention;

FIG. 5B is a sectional view of the polishing pad according to the first embodiment of the present invention;

FIGS. 6A and 6B are views for describing one-mode of pad groove walls of the polishing pad according to the present invention;

FIG. 7 is a sectional view of a polishing pad according to a second embodiment of the present invention;

FIG. 8 is a top view of a polishing pad according to a third embodiment of the present invention;

FIG. 9 is a sectional view of the polishing pad according to the third embodiment of the present invention;

FIG. 10 is a top view of a polishing pad according to a fourth embodiment of the present invention; and

FIG. 11 is a sectional view of the polishing pad according to the fourth embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes.

First Embodiment

FIGS. 5A and 5B show sectional views of a polishing pad 30 according to a first embodiment of the present invention. The polishing pad 30 is made of a synthetic resin such as polyurethane. Further, the polishing pad 30 has pad grooves 32 formed in grid like fashion like in a polishing pad 6 shown in FIG. 3. The pad grooves 32 are formed by mechanical machining. Further, FIG. 5A is a sectional view taken along the line A-A′ of FIG. 3. FIG. 5B is a sectional view taken along the line B-B′ of FIG. 3. Further, a sectional shape of the pad groove 32 is a U-shape. A pad groove base portion 32 a is a flat plane. Pad groove walls 32 b are walls perpendicular to the pad groove base portion 32 a. This sectional shape is one example as described after.

A dimension of a groove width W30 of the pad groove 32 is the same as that of the pad groove 32 in any place on the pad. Further, a pitch P30 of the pad grooves 32 is also constant.

From a center 30 c of the polishing pad 30 toward an outer edge thereof, a depth of the pad groove 32 increases. That is, in the vicinity of the center 30 c of the polishing pad 30, the pad groove 32 has a depth D2, in a middle portion between the center 30 c and the outer edge, the pad groove 32 has a depth D3, and in the outer edge, the pad groove 32 has a depth D4. As shown in FIG. 5B, when a surface of any pad grooves 32 is viewed in section, it is understood that the pad grooves 32 has an inclined surface 32 a′ toward the outer edge of the polishing pad 30 with the center 30 c of the polishing pad 30 being a highest point.

Note that, the polishing pad 30 is composed of two layers, that is, an upper layer polishing pad 30 a and a lower layer polishing pad 30 b. The pad grooves 32 are formed in the upper layer polishing pad 30 a.

As described above, the polishing pad 30 has a structure in which the depth of the pad groove 32 increases from the center 30 c toward the outer edge. Accordingly, with a centrifugal force caused by rotation of a polishing platen 4 and also with a function of the inclined surface 32 a′ of the pad groove base portion 32, a slurry 16 and shavings produced by the polishing pad 30 can easily be discharged. The outer edge of the polishing pad 6 corresponds to lower portions of the inclined surface 32 a′, so the slurry 16 and the shavings flow toward the outer edge. When the slurry 16 and the shavings are easily discharged, anew slurry 16 supplied from a slurry nozzle 14 is supplied to a polishing surface of a wafer 12, thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves 32 formed in the polishing pad 30, holes may further be formed therein.

A CMP apparatus 2 including the polishing pad 30 is used to polish the wafer 12 in the following manner. First, the polishing pad 30 is adhered on an upper surface of the polishing platen 4. A spindle carrier 8 retains the wafer 12 and the spindle carrier 8 presses the wafer 12 to the polishing pad 30 at a constant load. Through the slurry nozzle 14, from a storage container (not shown) of the slurry 16, the slurry 16 is supplied to the upper surface of the polishing pad 30 continuously or intermittently. The polishing platen 4 rotates at a constant rotation speed and the spindle carrier 8 also rotates at a constant rotation speed.

FIGS. 6A and 6B are views for describing another example of pad groove walls of the polishing pad 30 according to the present invention. FIGS. 6A and 6B are examples of pad groove 41 illustrating a shallow pad groove 44 and deep pad groove 46. In correspondence with the above description made with reference to FIGS. 5A and 5B, the shallow pad groove 44 having a depth D2′ indicates the pad groove 41 in the vicinity of the center 30 c of the polishing pad 32 and the deep pad groove 46 having a depth D4′ indicates the pad groove 41 in the vicinity of the outer edge of the polishing pad 30. A width W3 of a base portion of the shallow pad groove 44 is smaller than a width W2 of an upper portion thereof, and pad groove walls 44 a form inclined surfaces. Further, a width W5 of a base portion of the deep pad groove 46 is smaller than a width W4 of an upper portion thereof, and pad groove walls 46 a form inclined surfaces. In this case, the width W2 and the width W4 of the upper portions have the same dimension. The pad grooves 41 are formed by mechanical machining.

As described above, the pad groove walls 44 a and 46 a of the pad grooves 41 form the inclined surfaces, thereby making the slurry 16 and the shavings produced by the polishing pad 30 difficult to remain in the pad grooves 41 and easily discharged. That is, the inclined surfaces of the pad groove walls 44 a and 46 a have an effect of preventing generation of the micro scratches on the wafer 12.

Second Embodiment

FIG. 7 shows a sectional view of a polishing pad 40 according to a second embodiment of the present invention. The polishing pad 40 is made of a synthetic resin such as polyurethane. Further, the polishing pad 40 has pad grooves 42 formed in a grid like fashion like in the polishing pad 6 shown in FIG. 3. The pad grooves 42 are formed by mechanical machining. Further, FIG. 7 is a sectional view taken along the line A-A′ of FIG. 3. Further, a sectional shape of the pad groove 42 is a U-shape. A pad groove base portion 42 a is a plane. Pad groove walls 42 b are walls perpendicular to the pad groove base portion 42 a. Note that, as shown in FIG. 6, in a sectional shape of the pad groove 42, the pad groove walls 42 b′ may form the inclined surfaces.

A dimension of a groove width W40 of the pad groove 42 is the same as that of the pad groove 42 in any place. Further, a pitch P40 of the pad grooves 42 is also constant.

The polishing pad 40 has a structure in which the pad grooves 42 are divided from an outer edge side into groups of a first pad grooves 40 d, a second pad grooves 40 e, a third pad grooves 40 f, a fourth pad grooves 40 g, and a fifth pad grooves 40 h, and a groove depth of the each group is set for each group. A depth D5 of the first pad grooves 40 d is the largest. The nearer the group is to a center 40 c, the smaller the groove depth is. For example, the third pad grooves 40 f have a depth D6. A depth D7 of the fifth pad grooves 40 h is the smallest.

Note that, the polishing pad 40 is composed of two layers, that is, an upper layer polishing pad 40 a and a lower layer polishing pad 40 b. The pad grooves 42 are formed in the upper layer polishing pad 40 a. Each of the upper layer polishing pad 40 a and the lower layer polishing pad 40 b has a thickness of about 1 to 2 mm. The depth D5 of the first pad grooves 40 d is 80% of a thickness of the upper layer polishing pad 40 a. The depth D6 of the third pad grooves 40 f is 60% of the thickness of the upper layer polishing pad 40 a. The depth D7 of the fifth pad grooves 40 h is 40% of the thickness of the upper layer polishing pad 40 a.

As described above, the polishing pad 40 has a structure in which the depth of the pad grooves 42 stepwisely increases from the center 40 c towards the outer edge. Accordingly, with a centrifugal force caused by rotation of the polishing platen 4 and also with a function of the depth of the pad grooves 42 increasing stepwisely, the slurry 16 and shavings produced by the polishing pad 40 can easily be discharged. When the slurry 16 and the shavings are easily discharged, a new slurry 16 supplied from the slurry nozzle 14 is supplied to the polishing surface of the wafer 12, thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves 42 formed in the polishing pad 40, holes may further be formed therein.

Third Embodiment

FIG. 8 is a top view of a polishing pad 50 according to a third embodiment of the present invention. The polishing pad 50 is made of a synthetic resin such as polyurethane. Pad grooves 52 are arranged so as to extend radially from a center of the polishing pad 50. The pad grooves 52 are formed by mechanical machining. Further, the pad grooves 52 has a U-shaped section (not shown). The pad grooves section may be inclined surface as shown in FIGS. 6A and 6B but U-shaped section.

FIG. 9 is a sectional view of the polishing pad 50 according to the third embodiment of the present invention. FIG. 9 is a sectional view taken along the line C-C′ of FIG. 8. From a center 50 c of the polishing pad 50 toward an outer edge of the polishing pad 50, a pad groove base portion 52 a forms an inclined surface. Note that, the polishing pad 50 is composed of two layers, that is, an upper layer polishing pad 50 a and a lower layer polishing pad 50 b. The pad grooves 52 are formed in the upper layer polishing pad 50 a.

As described above, the polishing pad 50 has a structure in which a depth of the pad groove 52 increases from the center 50 c toward the outer edge. Accordingly, with a centrifugal force caused by rotation of the polishing platen 4 and also with a function of the pad groove 52 having the depth increasing, the slurry 16 and shavings produced by the polishing pad 50 can easily be discharged. When the slurry 16 and the shavings are easily discharged, a new slurry 16 supplied from the slurry nozzle 14 is supplied to the polishing surface of the wafer 12, thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves 52 formed in the polishing pad 50, holes may further be formed therein.

Fourth Embodiment

FIG. 10 is a top view of a polishing pad 60 according to a fourth embodiment of the present invention. The polishing pad 60 is formed of a synthetic resin such as polyurethane. Pad grooves 62 are arranged so as to extend spirally from a center of the polishing pad 60. The pad grooves 62 are formed by mechanical machining. Further, the pad groove 62 has a U-shaped section (not shown). However, as shown in FIG. 6, pad groove walls may form inclined surfaces.

FIG. 11 is a sectional view of the polishing pad 60 according to the fourth embodiment of the present invention. FIG. 11 is a sectional view taken along the line D-D′ of FIG. 10. From a center 60 c of the polishing pad 60 toward an outer edge of the polishing pad 60, a pad groove base portion 62 a forms an inclined surface. Note that, the polishing pad 60 is composed of two layers, that is, an upper layer polishing pad 60 a and a lower layer polishing pad 60 b. The pad grooves 62 are formed in the upper layer polishing pad 60 a.

As described above, the polishing pad 60 has a structure in which from the center 60 c to the outer edge, a depth of the pad groove 62 increases. Accordingly, with a centrifugal force caused by the rotation of the polishing platen 4 and also with a function of the pad groove 62 having the depth increasing, the slurry 16 and shavings produced by the polishing pad 60 are easily discharged. When the slurry 16 and the shavings are easily discharged, a new slurry 16 supplied by the slurry nozzle 14 is supplied to the polishing surface of the wafer 12, thereby making it possible to prevent generation of micro scratches. Note that, in addition to the pad grooves 62 formed in the polishing pad 60, holes may further be formed therein.

In the above description, the first to fourth embodiments are described. However, the first to fourth embodiments may be employed in any combination. 

1. A polishing pad, having a plurality of grooves extending from center to edge of the polishing pad, wherein the groove has a depth becoming larger from the center of the polishing pad toward edge portion and largest at the edge portion.
 2. A polishing pad as claimed in claim 1, wherein the depths of the groove is gradually increased.
 3. A polishing pad as claimed in claim 1, wherein the depths of the groove is stepwisely increased.
 4. A polishing pad as claimed in claim 1, wherein the plurality of grooves are provided in grid like fashion onto the surface of the polishing pad.
 5. A polishing pad as claimed in claim 1, wherein the plurality of grooves are provided onto the surface of the polishing pad radially from the center of the polishing pad.
 6. A polishing pad as claimed in claim 1, wherein the plurality of grooves are provided onto the surface of the polishing pad in a form of curved line extending from center to edge of the polishing pad.
 7. A polishing pad as claimed in claim 1, wherein the grooves are taper-shape having bottom portions that are narrower than their top portions.
 8. A polishing apparatus, comprising: a polishing pad; a polishing platen which is rotatable and on which the polishing pad is placed; a substrate retaining mechanism; and a supplying mechanism for supplying a polishing agent on upper surface of the polishing pad, wherein the polishing pad has a plurality of grooves extending from center to edge of the polishing pad; the grooves have a depth gradually becoming larger from the center of the polishing pad toward edge portion and largest at the edge portion.
 9. A method of polishing a substrate, comprising the steps of: placing the polishing pad according to claim 1 on a polishing platen; retaining the substrate; pressing the substrate to the polishing pad; supplying a polishing agent to upper surface of the polishing pad; rotating the polishing platen; and rotating the substrate.
 10. A polishing pad comprising a body having a center part and a peripheral part, and a plurality of grooves selectively formed in the body with a first depth at the center part and a second depth at the peripheral part, the first depth being smaller than the second depth.
 11. The pad as claimed in claim 10, wherein the first depth is changed stepwisely from the second depth.
 12. The pad as claimed in claim 10, wherein the first depth is changed gradually from the second depth. 